Synanthropic Wildlife Associated with Livestock Production as Carriers of High Priority Antimicrobial Resistances

Introduction: At the wildlife-livestock interface, wildlife have been found to carry antimicrobial resistant (AMR) bacteria and genes, which may promote the development and exchange of AMR between livestock and the environment.  Thus, wildlife incursion into agricultural facilities that are major foci of AMR, such as concentrated animal feeding operations (CAFOs), is of particular concern.  Efforts to understand the prevalence and extent of AMR in specific wildlife carriers are needed to profile AMR emergence, evaluate transmission dynamics, and identify mitigation points for wildlife managers and producers.

Purpose: This study assessed AMR indicator bacteria (Escherichia coli and Enterococcus sp.) collected from CAFO-associated wildlife (primarily rodents and raccoons) with similar bacteria from cattle and the CAFO environment, emphasizing the detection of multiple types of AMR classified by the United States Centers for Disease Control and Prevention as “Urgent, Serious, and Concerning Threats.”

Methods: A total of 726 wildlife fecal, 195 cattle fecal, and 154 environmental samples were collected from five CAFOs located in Northern Colorado.  An isolation procedure which incorporated sub-minimal inhibitory concentrations of high-priority antibiotics into microbiological growth media was used to screen these samples for the AMR indicator bacteria.  Species identification of isolates was confirmed by MALDI biotyping.  Antimicrobial susceptibility determinations were achieved using the disk diffusion assay to 18 antibiotics for E. coli and 13 antibiotics for Enterococcus sp. isolates.

Results: From the fecal and environmental samples, MALDI Biotyping confidently identified (Biotyping score ≥ 2.0) 555 AMR indicator bacteria.  The extent of AMR was associated with host organism, CAFO, and the specific Enterococcus sp.  Comparison of antimicrobial susceptibly biosignatures indicated that specific isolates were circulating between cattle, wildlife, and among CAFO sites.

Significance: This study demonstrates that synanthropic wildlife may contribute to the exchange and dissemination of AMR in livestock production.